A combinatorial benzodiazepine library was probed for pro-apoptotic members. These experiments yielded a promising family of novel cytotoxic molecules, the lead compound of which is designated Bz-423. Bz-423 has a novel mechanism of action and target relative to known apoptotic small molecules and is active against tumor cell growth both in vitro and in vivo. Bz-423 induces a mitochondria-dependent apoptotic pathway, in which the primary signaling event is a robust increase in reactive oxygen. Experiments with isolated mitochondria and screening of a phage display cDNA library for binding partners identified the oligomycin sensitivity conferring protein (OSCP) as a target. Experiments with purified recombinant OSCP resulted in binding isotherms indicating nanomolar affinity, strongly supporting the target's validity. We propose experiments aimed at elucidating critical elements of the mechanism of action related to this target in an effort to determine the therapeutic potential of this class of agents against cancer. Experiments will validate this target at the biochemical and cellular levels. The potential of these compounds to block proliferation and the mechanism leading to this alternative response will be explored. Experiments using an animal model of tumor growth will validate the molecular target and pharmacodynamic responses in vivo and relate these to effects on tumor growth. These studies form the basis of a platform of research to identify the therapeutic use of this new class of molecules and to evaluate the possibility that the OSCP is a tractable drug target for cancer.